Magnesium- and strontium-co-substituted hydroxyapatite: the effects of doped-ions on the structure and chemico-physical properties

The present study is aimed at investigating the contribution of two biologically important cations, Mg²⁺ and Sr²⁺, when substituted into the structure of
hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂,HA). The substituted samples were synthesized by an aqueous precipitation method that involved the addition of Mg²⁺- and Sr²⁺-containing precursors to partially replace Ca²⁺ ions in the apatite structure. Eight substituted HA samples with different concentrations of single (only Mg²⁺) or combined (Mg²⁺ and Sr²⁺) substitution of cations have been investigated and the results compared with those of pure HA. The obtained materials were characterized by X-ray powder diffraction, specific surface area and porosity measurements (N₂ adsorption at 77 K), FT-IR and Raman spectroscopies and scanning electron microscopy. The results indicate that the co-substitution gives rise to the formation of HA and ß-TCP structure types, with a variation of their cell parameters and of the crystallinity degree
of HA with varying levels of substitution. An evaluation of the amount of substituents allows us to design and prepare BCP composite materials with a desired HA/ß-TCP ratio.